1. Field of the Invention
The present invention relates to a magnetic mixture, and more particularly, to a magnetic mixture of two or more kinds of soft magnetic material powders which are uniformly mixed with each other, which mixture is useful as a raw material for the production of products having the intended magnetic properties.
2. Prior Art
Powder magnetic cores are frequently used in a smoothing choke coil provided on the direct current output side of a switching regulator, a reactor of an active filter provided in an inverter controller, and the like.
The powder magnetic core is generally produced by adding a predetermined amount of an insulating binder such as water glass to a powder of a soft magnetic alloy having predetermined magnetic properties and by subjecting the resultant mixture to press molding.
As a raw material for a powder magnetic core, soft magnetic alloys such as an Fexe2x80x94Si alloy, an Fexe2x80x94Sixe2x80x94Al alloy and an Fexe2x80x94Ni alloy are used. Pure iron, other than an alloy, having high saturation magnetization is also used.
In the preparation of these alloys, the aforementioned constituent elements are added to Fe serving as a base element in such a manner that a predetermined composition ratio is attained.
When the composition ratio of the constituent elements of the alloy varies, magnetic properties of the alloy also vary. At a particular composition ratio, there appears a significant point in magnetic properties of the alloy, i.e., a significant magnetic property, such that the saturation magnetization, permeability, magnetostriction, magnetic anisotropy constant or the like has a local maximum, a local minimum, or a value of substantially zero.
For example, in the case of the Fexe2x80x94Sixe2x80x94Al alloy, when the composition ratio of Si or Al is varied, the degree to which the significant magnetic properties that manetostriction becomes substantially zero and the permeability has a local maximum are exhibited also vary. At the composition ratio where Si is 9.0 to 10.0% by weight and Al is 5.0 to 6.0% by weight, both the significant magnetic properties appear, and hence an alloy having the magnetostriction of substantially zero and a maximum value of permeability can be obtained. A representative example of such an alloy has the composition of Fe-9.5% Si-5.5%Al, which is a soft magnetic alloy generally called Sendust. By using this alloy, it is possible to produce a magnetic core having a small core loss.
In this manner, a soft magnetic alloy for use as a raw material for a powder magnetic core is prepared: to have a significant point in magnetic property by determining the composition ratio of the constituent elements in accordance with the intended properties of the powder magnetic core.
For example, among the Fexe2x80x94Si alloys, there can be mentioned an Fe-6.5% Si alloy having the significant property that the magnetostriction is substantially zero. As the Fexe2x80x94Sixe2x80x94Al alloy, Sendust having the above-mentioned composition can be mentioned. As the Fexe2x80x94Ni alloy, an Fe-80% Ni-2% Mo alloy generally called PC permalloy can be mentioned, which has both the significant property that the magnetostriction is substantially zero and the significant property that permeability has a local maximum. As the Fexe2x80x94Co alloy, there can be mentioned an Fe-49% Co-2% V alloy and an Fe-50% Co alloy, which are generally called permendur and exhibit the significant property that the saturation magnetization has a local maximum.
A powder magnetic core produced using a powder of Sendust has a low coercive force, achieving such properties that the core loss is reduced and the permeability is high. However, Sendust has low saturation magnetization, exhibiting low permeability when a large current flows therethrough. In some application fields, the powder magnetic core produced solely from Sendust may have unsatisfactory performance in practical use.
Recently, powder magnetic cores have been sometimes requested to have essential magnetic properties by retaining significant magnetic properties of the raw material, whereas magnetic properties other than essential magnetic properties may be maintained in the cores at individual grade levels. However, by use of the conventional raw material prepared to exhibit one significant property, the resultant powder magnetic core also exhibits one significant property. Thus, the above-mentioned demand cannot be met. For example, such a demand that the powder magnetic core must have a plurality of essential magnetic properties, e.g., core loss and saturation magnetization, or core loss and permeability, cannot be satisfied.
It is an object of the present invention to provide a magnetic mixture in which, among the significant magnetic properties of a raw material (soft magnetic alloy) for a powder magnetic core to be produced, those significant magnetic properties which are required of the powder magnetic core are retained in the magnetic mixture, although unnecessary significant magnetic properties are permitted to be deteriorated.
It is another object of the present invention to provide a magnetic mixture which can be produced simply by uniformly mixing at least two kinds of soft magnetic material powders, at lower costs as compared to the conventional magnetic mixture, and which makes it possible to produce a powder magnetic core at a high degree of freedom of design.
To attain the above objects, the present invention provides a magnetic mixture (hereinafter, referred to as xe2x80x9cmagnetic mixture 1xe2x80x9d) comprising at least two kinds of powders which are uniformly mixed with each other, wherein constituent elements of each of the powders have a particular composition ratio to exhibit a significant point in magnetic property. Magnetic properties of each of the powders are retained in the magnetic mixture, and the magnetic mixture exhibits, as a whole, a soft magnetic property.
Further, the present invention provides a magnetic mixture (hereinafter, referred to as xe2x80x9cmagnetic mixture 2xe2x80x9d) comprising at least one kind of soft magnetic material powder whose constituent elements having a particular composition ratio to exhibit a significant point:in magnetic property; and at least one different kind of soft magnetic material powder which is uniformly mixed with the at least one kind of soft magnetic material powder, wherein magnetic properties of each of the powders are retained in the magnetic mixture, and the magnetic mixture exhibits, as a whole, a soft magnetic property.
Further, there are provided magnetic mixture 1 and magnetic mixture 2 each further comprising at least one insulating material which is uniformly mixed thereinto.
Furthermore, according to the present invention, a magnetic mixture is provided, which comprises two or three kinds of powders which are uniformly mixed with each other, wherein the powders are selected from the group. consisting of a powder of an Fe-(3.0xc2x10.5)% Si alloy, a powder of an Fe-(6.5xc2x10.5)% Si alloy and a powder of an Fe-(9.5xc2x10.5)% Si-(5.5xc2x10.5)% Al alloy. Further, a magnetic mixture is provided, which comprises the just-mentioned magnetic mixture of 70% by weight or more and a powder of pure iron of 30% by weight or less.
First, a magnetic mixture 1 is described.
The magnetic mixture 1 is obtained by uniformly mixing together two or more kinds of soft magnetic material powders.
More specifically, as the soft magnetic material, a soft magnetic alloy is used, which must exhibit not only a soft magnetic property but also a significant point in magnetic property, i.e., a significant magnetic property, when its constituent elements have a particular composition ratio. Examples of such soft magnetic alloys include one that exhibits, when it has a particular composition, a significant property such that the magnetostriction or the magnetic anisotropy constant has a value of substantially zero, or the permeability has a local maximum or the coercive force has a local minimum, or the saturation magnetization has a local maximum.
More strictly, when it is assumed that a magnetic property f of the soft magnetic material is represented by f(C1, C2, . . . , cn), where C1, C2, . . . , cn denote the composition ratios of individual constituent elements a1, a2, . . . , and an of the soft magnetic material, the soft magnetic material has those composition ratios of constituent elements which satisfy the following equation:
f(C1, C2, . . . , cn)=0,
or             ∂      f              ∂              c        i              =  0
wherein i is 1, 2, . . . , n.
It is noted that variations are allowed so long as they fall within the industrially acceptable range.
As the soft magnetic alloys, by way of example, the following can be mentioned.
As the Fexe2x80x94Si alloy, there can be mentioned an Fe-6.5% Si alloy which exhibits a significant point in magnetic property, i.e., a significant property, such that the magnetostriction has a value of substantially zero.
As the Fexe2x80x94Sixe2x80x94Al alloy, there can be mentioned an Fe-9.5% Si-5.5% Al (Sendust) which simultaneously exhibits significant magnetic properties such that the magnetostriction and the magnetic anisotropy constant have a value of substantially zero, the permeability has a local maximum, and the coercive force has a local minimum.
As the Fexe2x80x94Ni alloy, there can be mentioned an Fe-80% Ni-2% Mo (PC permalloy) which simultaneously exhibits significant properties such that the magnetostriction is substantially zero and the permeability has a local maximum, and an Fe-46% Ni which exhibits a local maximum of the permeability.
As the Fexe2x80x94Co alloy, there can be mentioned permendur (Fe-49% Co-2% V, Fe-50% Co) which exhibits significant properties such that the saturation magnetization has a local maximum larger than that of pure iron and the permeability has a local maximum, and Fe-35% Co which exhibits a maximum value of the saturation magnetization.
Pure iron exhibits a maximum value of the saturation magnetization, and the saturation magnetization of pure iron is lowered when other elements are added thereto.
To be noted, the wording xe2x80x9cmagnetostriction is substantially zeroxe2x80x9d used here means that the magnetostriction having an absolute value of zero is optimal, but may vary within the industrially acceptable range.
The magnetic mixture 1 is produced by uniformly mixing together powders of the above-mentioned two or more soft magnetic alloys.
In this case, the alloy powders to be mixed are appropriately selected in accordance with the magnetic properties required of the powder magnetic core to be produced.
For example, when essential magnetic properties required of the powder magnetic core to be produced are such that the magnetostriction is zero and the permeability and the saturation magnetization have appropriate values, powders of two or more kinds of soft magnetic alloys, each exhibiting the significant property such that the magnetostriction is zero, are selected and uniformly mixed with each other.
For example, when a powder of an Fe-6.5% Si alloy and a powder of an Fe-9.5% Si-5.5% Al (Sendust) are uniformly mixed with each other, the powder magnetic core produced using the resultant mixture has the magnetostriction of zero, irrespective of the mixing ratio of the alloys. In this case, the permeability which is another significant property of Sendust powder is lowered by the dilute effect of the presence of the Fe-6.5% Si powder.
The mixture obtained by mixing together the above-mentioned two kinds of powders contains Fe, Si and Al as constituent elements, and the ratio of quantity of these elements varies depending on the mixing ratio of them. On the other hand, even when a powder of an Fexe2x80x94Sixe2x80x94Al alloy having that composition ratio of the constituent elements which is the same as the ratio of quantity of the just-mentioned mixture is used, the resultant powder magnetic core does not exhibit the significant magnetic property, i.e., the specific point in magnetic properties, such that the magnetostriction is zero.
When a powder of pure iron and a powder of permendur which have a common significant property in respect of the saturation magnetization are mixed with each other, the common significant property is retained in the powder magnetic core produced using the resultant mixture, whereby an inexpensive soft magnetic material exhibiting high saturation magnetization can be provided.
As mentioned above, the magnetic mixture 1 of the present invention is obtained by uniformly mixing together two or more kinds of alloy powders each exhibiting a particular significant property, and is featured in that the magnetic properties of respective alloy powders observed before mixing are retained as they are, and that the mixture exhibits, as a whole, a soft magnetic property.
Therefore, the ratio of the constituent elements of each soft magnetic alloy powder should not be changed by subjecting the magnetic mixture 1 to diffusion sintering at a high temperature, carburizing, decarburization, or the like.
It is preferred that at least one insulating material is uniformly mixed with the magnetic mixture 1, to improve the electric resistivity and suppress the eddy current loss.
As the insulating material, an insulating material having a binding ability is mixed, for example. During the pressing, the powders of the magnetic mixture 1 are bound together to be formed into a desired shape, and insulation between the particles is achieved so that an eddy current is suppressed when the powder magnetic core is in actual use.
As such an insulating material, there can be mentioned water glass; insulating materials of a type having a binding ability, such as phenolic resins, nylon resins, epoxy resins, silicone resins; other insulating materials or oxides such as silica, alumina, zirconia and magnesia; and mixtures thereof.
Next, the aforementioned magnetic mixture 2 of the present invention is described.
The magnetic mixture 2 is obtained by uniformly mixing a powder of at least one, preferably two or more kinds of soft magnetic materials, each exhibiting a significant magnetic property when it has a predetermined composition, with a different kind of soft magnetic material, more specifically, with one or more different kinds of powders of soft magnetic alloys.
The different kind of powder may be a powder exhibiting a significant magnetic property as in the case of magnetic mixture 1 or a powder exhibiting no significant property. That is, the different kind of powder may be any alloy material powder as long as it has a soft magnetic property.
By way of examples, such powders include a powder of an Fexe2x80x94Si alloy such as an Fe-4% Si alloy; a powder of an Fexe2x80x94Sixe2x80x94Al alloy such as an Fe-3% Si-2% Al alloy; a powder of an Fexe2x80x94Ni alloy such as an Fe-65% Ni alloy. Of these, an Fe-4% Si alloy powder is preferred because it is relatively inexpensive.
With respect to the magnetic properties of the magnetic mixture 2 basically comprised of a material powder which exhibits a significant property, this significant property of the material powder is retained in the mixture 2. The mixture 2 further contains a different kind of soft magnetic powder such as an inexpensive soft magnetic powder, so that the mixture 2 is low-priced as a whole.
As for the magnetic mixture 2, it is preferred that an insulating material is uniformly mixed for the same reason as that mentioned on the magnetic mixture 1.